diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,18 @@
+# 0.6.2.0
+
+## Added features
+
+* Added instances for `BeamSqlBackendIsString Postgres (CI String)` and
+  `BeamSqlBackendIsString Postgres (CI Text)`, allowing the use of `toTsVector`
+  over colums of type `citext` (#818)
+* Exposed the functionality to implement user-defined extensions via
+  `Database.Beam.Postgres.Extensions` (#819)
+
+## Bug fixes
+
+* Fixed an issue where using `pgSelectWith` with no common-table expressions
+  would lead to an invalid SQL query at runtime.
+
 # 0.6.1.0
 
 ## Added features
@@ -17,7 +32,7 @@
   role attribute and is the appropriate choice when the client and
   server are on different hosts — see
   `Database.Beam.Postgres.Extensions.Copy.Stream`.
-  
+
 ## Bug fixes
 
 * Fixed an issue where a window function applied over the result of `nub_` (or
diff --git a/Database/Beam/Postgres/Connection.hs b/Database/Beam/Postgres/Connection.hs
--- a/Database/Beam/Postgres/Connection.hs
+++ b/Database/Beam/Postgres/Connection.hs
@@ -9,7 +9,6 @@
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE OverloadedStrings #-}
-{-# LANGUAGE CPP #-}
 {-# LANGUAGE BangPatterns #-}
 
 module Database.Beam.Postgres.Connection
diff --git a/Database/Beam/Postgres/Extensions.hs b/Database/Beam/Postgres/Extensions.hs
--- a/Database/Beam/Postgres/Extensions.hs
+++ b/Database/Beam/Postgres/Extensions.hs
@@ -1,6 +1,5 @@
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE UndecidableInstances #-}
-{-# LANGUAGE CPP #-}
 
 -- | Postgres extensions are run-time loadable plugins that can extend Postgres
 -- functionality. Extensions are part of the database schema.
@@ -10,9 +9,29 @@
 -- the extension in a particular backend. @beam-postgres@ provides predicates
 -- and checks for @beam-migrate@ which allow extensions to be included as
 -- regular parts of beam migrations.
-module Database.Beam.Postgres.Extensions where
+module Database.Beam.Postgres.Extensions (
+  -- * Handling extensions
+  PgExtensionEntity,
+  getPgExtension,
 
+  -- * Defining extensions
+  IsPgExtension(..),
+  -- ** Helpers
+  PgExpr,
+  LiftPg,
+  funcE,
+
+  -- * Migrations
+  PgHasExtension(..),
+  pgCreateExtension,
+  pgDropExtension,
+  pgExtensionActionProvider,
+) where
+
 import           Database.Beam
+import           Database.Beam.Backend.SQL ( IsSql92ExpressionSyntax(..), IsSql92FieldNameSyntax(..),
+                                             IsSql99ExpressionSyntax, IsSql99FunctionExpressionSyntax(..)
+                                           )
 import           Database.Beam.Schema.Tables
 
 import           Database.Beam.Postgres.Types
@@ -122,6 +141,21 @@
                -> extension
 getPgExtension (DatabaseEntity (PgDatabaseExtension _ ext)) = ext
 
+-- *** Helpers to write postgres user-defined extensions
+
+-- | @since 0.6.2.0
+type PgExpr ctxt s = QGenExpr ctxt Postgres s
+
+-- | @since 0.6.2.0
+type family LiftPg ctxt s fn where
+  LiftPg ctxt s (Maybe a -> b) = Maybe (PgExpr ctxt s a) -> LiftPg ctxt s b
+  LiftPg ctxt s (a -> b) = PgExpr ctxt s a -> LiftPg ctxt s b
+  LiftPg ctxt s a = PgExpr ctxt s a
+
+-- | @since 0.6.2.0
+funcE :: IsSql99ExpressionSyntax expr => Text -> [expr] -> expr
+funcE nm = functionCallE (fieldE (unqualifiedField nm))
+
 -- *** Migrations support for extensions
 
 -- | 'Migration' representing the Postgres @CREATE EXTENSION@ command. Because
@@ -192,3 +226,4 @@
      pure (PotentialAction (HS.fromList [p extP]) mempty
                            (pure (MigrationCommand cmd MigrationKeepsData))
                            ("Unload the postgres extension " <> ext) 1)
+
diff --git a/Database/Beam/Postgres/Extensions/Internal.hs b/Database/Beam/Postgres/Extensions/Internal.hs
deleted file mode 100644
--- a/Database/Beam/Postgres/Extensions/Internal.hs
+++ /dev/null
@@ -1,17 +0,0 @@
-module Database.Beam.Postgres.Extensions.Internal where
-
-import Data.Text (Text)
-
-import Database.Beam
-import Database.Beam.Backend.SQL
-import Database.Beam.Postgres
-
-type PgExpr ctxt s = QGenExpr ctxt Postgres s
-
-type family LiftPg ctxt s fn where
-  LiftPg ctxt s (Maybe a -> b) = Maybe (PgExpr ctxt s a) -> LiftPg ctxt s b
-  LiftPg ctxt s (a -> b) = PgExpr ctxt s a -> LiftPg ctxt s b
-  LiftPg ctxt s a = PgExpr ctxt s a
-
-funcE :: IsSql99ExpressionSyntax expr => Text -> [expr] -> expr
-funcE nm args = functionCallE (fieldE (unqualifiedField nm)) args
diff --git a/Database/Beam/Postgres/Extensions/UuidOssp.hs b/Database/Beam/Postgres/Extensions/UuidOssp.hs
--- a/Database/Beam/Postgres/Extensions/UuidOssp.hs
+++ b/Database/Beam/Postgres/Extensions/UuidOssp.hs
@@ -10,8 +10,7 @@
 import           Data.UUID.Types (UUID)
 
 import           Database.Beam
-import           Database.Beam.Postgres.Extensions
-import           Database.Beam.Postgres.Extensions.Internal
+import           Database.Beam.Postgres.Extensions ( LiftPg, IsPgExtension(..), funcE )
 
 -- | Data type representing definitions contained in the @uuid-ossp@ extension
 data UuidOssp = UuidOssp
diff --git a/Database/Beam/Postgres/Full.hs b/Database/Beam/Postgres/Full.hs
--- a/Database/Beam/Postgres/Full.hs
+++ b/Database/Beam/Postgres/Full.hs
@@ -2,7 +2,6 @@
 {-# LANGUAGE UndecidableInstances #-}
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE TupleSections #-}
-{-# LANGUAGE CPP #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE TypeOperators #-}
 
@@ -71,6 +70,8 @@
 import           Control.Monad.State.Strict (evalState)
 import           Control.Monad.Writer (runWriterT)
 
+import           Data.List.NonEmpty (nonEmpty)
+import qualified Data.List.NonEmpty as NonEmpty
 import           Data.Kind (Type)
 import           Data.Proxy (Proxy(..))
 import qualified Data.Text as T
@@ -289,18 +290,21 @@
 --
 -- @beam-core@ offers 'selectWith' to produce a top-level 'SqlSelect'
 -- but these cannot be turned into 'Q' objects for use within joins.
---
--- The 'pgSelectWith' function is more flexible and indeed
--- 'selectWith' for @beam-postgres@ is equivalent to se
+-- The 'pgSelectWith' function is more flexible.
 pgSelectWith :: forall db s res
               . Projectible Postgres res
              => With Postgres db (Q Postgres db s res) -> Q Postgres db s res
 pgSelectWith (CTE.With mkQ) =
-    let (q, (recursiveness, ctes)) = evalState (runWriterT mkQ) 0
+    let (q, (recursiveness, mctes)) = evalState (runWriterT mkQ) 0
         fromSyntax tblPfx =
-            case recursiveness of
-              CTE.Nonrecursive -> withSyntax ctes (buildSqlQuery tblPfx q)
-              CTE.Recursive -> withRecursiveSyntax ctes (buildSqlQuery tblPfx q)
+            case (recursiveness, nonEmpty mctes) of
+              (CTE.Nonrecursive, Just ctes) -> withSyntax (NonEmpty.toList ctes) (buildSqlQuery tblPfx q)
+              (CTE.Recursive, Just ctes) -> withRecursiveSyntax (NonEmpty.toList ctes) (buildSqlQuery tblPfx q)
+               -- If there are no subqueries, we don't want to generate
+               -- an empty 'WITH' statement, which would be malformed.
+               -- 
+               -- see: https://github.com/haskell-beam/beam/issues/760
+              (_, Nothing) -> buildSqlQuery tblPfx q
     in Q (liftF (QAll (\tblPfx tName ->
                            let (_, names) = mkFieldNames @Postgres @res (qualifiedField tName)
                            in fromTable (PgTableSourceSyntax $
@@ -309,7 +313,7 @@
                       (\tName ->
                            let (projection, _) = mkFieldNames @Postgres @res (qualifiedField tName)
                            in projection)
-                      (\_ -> Nothing)
+                      (const Nothing)
                       snd))
 
 -- | By default, Postgres will throw an error when a conflict is detected. This
diff --git a/Database/Beam/Postgres/Migrate.hs b/Database/Beam/Postgres/Migrate.hs
--- a/Database/Beam/Postgres/Migrate.hs
+++ b/Database/Beam/Postgres/Migrate.hs
@@ -60,7 +60,7 @@
 import           Control.Exception.Lifted (mask, onException)
 import           Control.Monad
 
-import           Data.Aeson hiding (json)
+import           Data.Aeson
 import           Data.Bits
 import           Data.ByteString (ByteString)
 import qualified Data.ByteString.Lazy as BL
diff --git a/Database/Beam/Postgres/PgCrypto.hs b/Database/Beam/Postgres/PgCrypto.hs
--- a/Database/Beam/Postgres/PgCrypto.hs
+++ b/Database/Beam/Postgres/PgCrypto.hs
@@ -9,8 +9,7 @@
 import Database.Beam
 import Database.Beam.Backend.SQL
 
-import Database.Beam.Postgres.Extensions
-import Database.Beam.Postgres.Extensions.Internal
+import Database.Beam.Postgres.Extensions( LiftPg, PgExpr, IsPgExtension(..), funcE )
 
 import Data.Int
 import Data.Text (Text)
diff --git a/Database/Beam/Postgres/PgSpecific.hs b/Database/Beam/Postgres/PgSpecific.hs
--- a/Database/Beam/Postgres/PgSpecific.hs
+++ b/Database/Beam/Postgres/PgSpecific.hs
@@ -9,7 +9,6 @@
 {-# LANGUAGE TypeApplications #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE PolyKinds #-}
-{-# LANGUAGE CPP #-}
 
 -- | Postgres-specific types, functions, and operators
 module Database.Beam.Postgres.PgSpecific
diff --git a/Database/Beam/Postgres/Types.hs b/Database/Beam/Postgres/Types.hs
--- a/Database/Beam/Postgres/Types.hs
+++ b/Database/Beam/Postgres/Types.hs
@@ -1,5 +1,5 @@
 {-# OPTIONS_GHC -fno-warn-orphans #-}
-
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE UndecidableInstances #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
@@ -184,6 +184,12 @@
 
 instance BeamSqlBackendIsString Postgres String
 instance BeamSqlBackendIsString Postgres Text
+
+-- | @since 0.6.2.0
+instance BeamSqlBackendIsString Postgres (CI String)
+
+-- | @since 0.6.2.0
+instance BeamSqlBackendIsString Postgres (CI Text)
 
 instance HasQBuilder Postgres where
   buildSqlQuery = buildSql92Query' True
diff --git a/beam-postgres.cabal b/beam-postgres.cabal
--- a/beam-postgres.cabal
+++ b/beam-postgres.cabal
@@ -1,5 +1,5 @@
 name:                 beam-postgres
-version:              0.6.1.0
+version:              0.6.2.0
 synopsis:             Connection layer between beam and postgres
 description:          Beam driver for <https://www.postgresql.org/ PostgreSQL>, an advanced open-source RDBMS
 homepage:             https://haskell-beam.github.io/beam/user-guide/backends/beam-postgres
@@ -23,16 +23,15 @@
                       Database.Beam.Postgres.Full
 
                       Database.Beam.Postgres.PgCrypto
+                      Database.Beam.Postgres.Extensions
                       Database.Beam.Postgres.Extensions.UuidOssp
 
                       Database.Beam.Postgres.TempTable
 
   other-modules:      Database.Beam.Postgres.Connection
                       Database.Beam.Postgres.Debug
-                      Database.Beam.Postgres.Extensions
                       Database.Beam.Postgres.Extensions.Copy.File
                       Database.Beam.Postgres.Extensions.Copy.Stream
-                      Database.Beam.Postgres.Extensions.Internal
                       Database.Beam.Postgres.PgSpecific
                       Database.Beam.Postgres.Types
 
@@ -54,7 +53,7 @@
                       monad-control        >=1.0  && <1.1,
                       mtl                  >=2.1  && <2.4,
                       conduit              >=1.2  && <1.4,
-                      aeson                >=0.11 && <2.3,
+                      aeson                >=0.11 && <2.4,
                       uuid-types           >=1.0  && <1.1,
                       case-insensitive     >=1.2  && <1.3,
                       scientific           >=0.3  && <0.4,
@@ -67,7 +66,7 @@
   default-language:   Haskell2010
   default-extensions: ScopedTypeVariables, OverloadedStrings, MultiParamTypeClasses, RankNTypes, FlexibleInstances,
                       DeriveDataTypeable, DeriveGeneric, StandaloneDeriving, TypeFamilies, GADTs, OverloadedStrings,
-                      CPP, TypeApplications, FlexibleContexts
+                      TypeApplications, FlexibleContexts
   ghc-options:        -Wall
                       -Widentities
                       -Wincomplete-uni-patterns
@@ -97,7 +96,7 @@
     beam-migrate,
     beam-postgres,
     bytestring,
-    hedgehog,
+    hedgehog >= 1.0,
     postgresql-simple,
     tasty-hunit,
     tasty,
diff --git a/test/Database/Beam/Postgres/Test.hs b/test/Database/Beam/Postgres/Test.hs
--- a/test/Database/Beam/Postgres/Test.hs
+++ b/test/Database/Beam/Postgres/Test.hs
@@ -1,10 +1,5 @@
-{-# LANGUAGE CPP #-}
 module Database.Beam.Postgres.Test where
 
-#if MIN_VERSION_base(4,12,0)
-import           Prelude hiding (fail)
-#endif
-
 import qualified Database.PostgreSQL.Simple as Pg
 
 import           Control.Exception (bracket)
@@ -13,18 +8,6 @@
 
 import           Data.ByteString (ByteString)
 import           Data.String
-
-#if MIN_VERSION_base(4,12,0)
-#if !MIN_VERSION_hedgehog(1,0,0)
-import           Control.Monad.Fail (MonadFail(..))
-import qualified Hedgehog
--- TODO orphan instances are bad
--- Would be easier to say 'build-depends: hedgehog >= 1.0',
--- but it's difficult to propagate to older Stackage snapshots
-instance Monad m => MonadFail (Hedgehog.PropertyT m) where
-    fail _ = Hedgehog.failure
-#endif
-#endif
 
 withTestPostgres :: String -> IO ByteString -> (Pg.Connection -> IO a) -> IO a
 withTestPostgres dbName getConnStr action = do